A conventional electric motor includes a stator and a rotor which is configured to rotate within the stator. One conventional stator uses a stack of laminations to support a set of windings. The laminations in combination with the windings form a set of electromagnets which is configured to produce a changing magnetic field to turn the rotor.
FIG. 1 shows a cross sectional view of a conventional brushless DC motor 20 having a stator 22 and a rotor 24. The stator 22 includes stator laminations 26 which extend around the rotor 24. The rotor 24 includes a rotor shaft 28 and permanent magnets 30 distributed around the shaft 28.
Each stator lamination 26 includes an outer ring portion 32 and stator teeth 34 which protrude inwardly from the outer ring portion 32 toward the rotor 24. The windings of the stator 22 are omitted from FIG. 1 for simplicity but typically wrap around the stator teeth 34 of the stator laminations 26 to form motor windings. Slots 36 separate the stator teeth 34.
As shown in FIG. 1, the depth (d) of the slots 36 is less than the overall radius (r) of the rotor 24, i.e., d<r. Additionally, the overall diameter DS1 of the stator is less than twice the overall diameter DR1 of the rotor 24. That is, 2*DR1>DS1. Furthermore, the general slot cross sectional area is typically greater than that of the stator tooth 34.
Also, for each stator tooth 34, the tooth flanks 38 (i.e., the tooth sides along their mid-sections 42) are parallel and flare away from each other at the tooth end 44 adjacent the rotor 24. In particular, the tooth corners at the end 44 extend into tips forming a shoe 46 which is substantially wider than the mid-section 42 of the tooth 34 when measured perpendicularly from a central axis of the stator tooth 34.